1. Field of the Invention
The present invention relates to a concentrator which can be plugged into a bus backplane to insert other devices connected to the bus into a token ring network having a primary and a secondary ring. More specifically the invention relates to a concentrator which is used alone or in conjunction with a second identical concentrator to provide a set of externally configurable datapaths for connecting the bus backplane with primary and secondary rings in the network.
2. Description of the Related Prior Art
The invention involves token ring networks, primarily networks that conform to the ANSI FDDI standards X3.148, X3.139 and X3T9.5 (currently in draft form). However, while the devices specifically described herein conform to these standards, the invention is also applicable to other token ring standards.
In a token ring network the stations or "nodes" on the network are connected in a loop in which information signals propagate in a single direction. Thus, signals sent from one node to another will ordinarily pass through a number of intervening nodes in the course of travel along the ring. This arrangement raises a number of issues when it is desired to add nodes to, or remove them from, the network.
Specifically, the ring must be physically broken and its operation interrupted in order to add or remove a node. This is further complicated by the nature of the transmission medium, e.g. optical fiber or copper wire, that interconnects the nodes.
These problems have been addressed by the use of concentrators which are connected into the token ring and provide electrical and/or optical connections to various devices that can operate as token ring nodes. In a concentrator, the signal pathways are electrical, and thus, they can be switched electrically. They can therefore be switched fast enough to insert the nodes or chains of nodes into, or remove them from, the token ring without significantly interrupting the signal flow in the ring. Also, since these nodes can be electrically connected to the concentrator, they need not be provided with fiber optic interfaces and this reduces their cost.
The concentrators may also be provided with connectors that enable them to be plugged into backplanes to which token ring nodes are connected, thereby facilitating the physical connections between these nodes and the concentrators.
There are a number of different node arrangements which must be accommodated by the concentrators and this has required the use of different concentrator designs for these arrangements. In turn, this requires the manufacture and stocking of different concentrators. The present invention is directed primarily to a reduction in the costs associated with these factors.
The ANSI FDDI standards support several different types of ports, namely, A ports, B ports, M ports and S ports. Each port accommodates a particular type of connection. For example, an A port connects to the incoming primary ring and the outgoing secondary ring of the token ring network, a B port connects to the outgoing primary ring and the incoming secondary ring, an M port which operates only on a concentrator and connects the concentrator to a station or to another concentrator connects to the same incoming and outgoing ring, and an S port which operates on a station or a concentrator and connects a concentrator to a single attachment station or a single attachment concentrator connects to the same incoming and outgoing ring. The operating characteristics of these ports are set forth in more detail in FDDI standard X3T9.5, which is currently in draft form, relevant portions of this draft standard are attached hereto as appendix A. Although the hardware for these ports is basically the same, firmware configures the ports for the particular uses. The FDDI standard permits connections between A ports and B ports and between M ports and either A ports and B ports. However, two M ports may not be connected together. What is needed is a concentrator with a number of ports and datapaths which can be readily configured to accommodate the connection of various arrangements of devices to the token ring network.